Story’s a hoot, on reflection (4)
I believe the answer is:
saga
'story's' is the definition.
(saga is a kind of story)
'a hoot on reflection' is the wordplay.
'hoot' becomes 'gas'.
'on reflection' says the letters should be written backwards.
'a'+'gas'='agas'
'agas' in reverse letter order is 'SAGA'.
(Other definitions for saga that I've seen before include "Account of great heroism" , "Chronicle; adventure" , "Long involved tale" , "Long heroic tale" , "Medieval Icelandic legend" .)